Increasing fuel cost and environmental concerns have pushed the automotive industry to gradually replace internal combustion engine (ICE) vehicles with hybrid electric (HEV) and fully electric vehicles (EV). However, the energy density of electric batteries is much less than that of fossil fuels. Thus, by changing the source of power from internal combustion engine to electric motor, it is necessary to minimize the losses in the driveline in order to maximize the range of EVs. Pure electric vehicles in the market are mostly equipped with a single ratio transmission with a trade-off between efficiency and dynamic performance, such as maximum speed, acceleration, and gradability.
Research indicates that using a multi-speed transmission for EVs can reduce the size of the electric motor and provide an appropriate balance between the efficiency and the dynamic performance. Currently used multi-speed transmissions for EVs such as Automated Manual Transmission (AMT), Automatic Transmission (AT), Dual Clutch Transmission (DCT), and Continuously Variable Transmission (CVT) were initially designed for ICE vehicles. Since ICEs cannot operate below certain speeds and their speed control during gear changes is not an easy task, the presence of clutches or torque convertors is inevitable for start-ups, idle running and gear changing. This, however, is not the case for EVs as electric motors are speed-controllable in a wide range of operating speeds.
Accordingly, it would be beneficial to exploit the characteristics of electric motors to design novel transmissions for EVs.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.